How to Use Surveying Equipment to Determine Land Boundaries | eBay How to Use Surveying Equipment to Determine Land Boundaries Share March 3, 2016 Surveying is the technique, profession, and science of determining the dimensions and contour of the Earth's surface. Using specialized surveying equipment , professional surveyors determine land boundaries for a variety of important reasons. One of the most common reasons for a consumer to acquire the assistance of a surveyor is the acquisition of a new piece of land, as it has to be legally determined where one person's property ends and another begins for government issued deeds. Additionally, surveyors work with cartographers to create accurate maps. Surveying has existed in one form or another for at least 5,000 years; virtually all of recorded human history and likely even beyond. The pyramids in Egypt and Stonehenge in England are believed to have been created with the assistance of an ancient surveyor. It is an essential element of civilized society. Working with a combination of skills derived from physics, engineering, law, and the mathematics, surveyors are well trained to accurately measure flat and three-dimensional points, as well as the distance and angles between them. Surveying Tools Surveying requires data from three primary components.

This includes the measurement of distance, angles, and elevation. There are several different types of survey tools but each tool is capable of providing the necessary data from one or more of the measurement types. The art of surveying remained relatively unchanged until the late 1990s. Since the advent of more technologically advanced survey equipment, such as global positioning systems and electronic measurement devices, the tools available to the surveyor have become greater and more enhanced. As a result, some of the older techniques, such as the use of chains and tape are falling out of favor. Rods Surveying rods are a popular piece of equipment for surveyors and contractors alike. They are commonly made out of aluminum or hardwood, with both options having pros and cons. Though there are several different types or rod, they all serve the same purpose. Rods are designed to measure the distance between two points, often in conjunction with other surveying tools. The survey rod is often held by one surveyor or an assistant, as the other surveyor takes initial measurements, using one or more type of measurement device. There are several different types of rod.

Description Level Rod Leveling rods are typically made from aluminum or hardwood; they must always be treated with care since small chips can lead to level reading errors Philadelphia Level Rod Features two sliding sections joined by a brass sleeve; can be used for measurements of to 13 feet; can be read with a level from a distance of up to 250 feet San Francisco Level Rod Similar to the Philadelphia rod; features three separate, sliding sections for extending or reducing length Direct Reading Rod Read directly through a telescope by the surveyor; also known as self-reading rods Direct Elevation Rod Has a graduated strip that revolves around the rod using rollers; features numbers in reverse order; capable of providing elevation readings without need for additional foresight and backsight calculations Target Rod Features a target, making it possible for the person holding the rod to double check the readings presented by the person handling them surveying instrument Rods are a common survey tool used to estimate distance. Though very important, rods are only one of the numerous tools used to take survey measurements. Tripods A necessary tool for any surveyor, the tripod provides a strong, balanced location on which to place certain types of survey tools. Tripods are commonly adjustable and may be made up of wood, aluminum, or fiberglass.

Though fiberglass makes a heavy load for toting from one job to another, aluminum and wood may swell or contract in certain weather conditions, slightly altering readings. Tripods come in two primary sizes, though they are adjustable. There are also tripod extensions available to add extra reach to older or smaller models. The tripod will typically feature either a flat or dome head. Tripods are a commonly recognized tool of surveying, as most surveyors spend a lot of time behind the tripod, glancing through various measurement tools to acquire their all-important measurements. Levels Levels are another common tool of the survey trade. Often used in conjunction with a sturdy tripod and various rods, the tool is typically just a level attached to a sort of telescope or laser. The telescope is used to extend sight line in all directions, offering a reference point from which to measure the various elevations. Just as there are multiple types of surveying rods, multiple styles of level exist. Hand Level The hand level features a metal sighting tube with an attached bubble tube on the top. The bubble tube is reflected with a prism inside the tube so that the surveyor can see the bubble and terrain at the same time; used for taping and rough determinations of elevation.

Abney Level The abney level functions as a type of hand level, but allows for rough estimates of vertical angles and slopes. Abney levels consist of a spirit level and sighting tube and are almost exclusively used by surveyors. Automatic Level The automatic level is a very common type of level for surveyors to use. It features a quick setup with a three-screw leveling head and can typically be identified by the bubble marked with a bullseye. To use the automatic level, the surveyor manually centers the bullseye bubble and from that point, a laser takes over to insure that the object remains level. Electronic or Laser Level An electronic or laser level transmits a visible laser beam or invisible infrared beam. These levels may feature either a single or rotating beam and are considered to be precise up to 1,000 feet. Common uses of the electronic or laser level include grading, excavating, and checking the depth of trenches. A professional surveyor may find use for several different types of levels, depending on the assignment. The most commonly used today are the automatic level and the electronic level. These advanced levels can be used for nearly any surveying task.

Laser Detector Laser detectors are needed when a laser level does not feature a beam that is visible to the human eye. The laser detector is attached to the rod, whether mounted or hand-held, and will move up and down in response to the laser beam. This gives the surveyor a clear idea of where the level beam is landing so that he or she may take accurate measurements Double Pentagonal Prism Often during construction work or surveying the surveyor needs to find a 90 degrees angle simply and effectively. The double pentagonal prism is a handheld device for locating these right triangles. The device features two prisms, of 90 and 180 degrees. The dual prisms allow for a wide field of sight, making it easy for a surveyor to locate measure cross sections and slopes with ease. Range Poles Range poles are a very common tool in the surveying world. They are used for sighting and marking ground points and lining up surveyors. Most range poles are six to ten feet in length and painted with alternating red and white stripes for easy sight.

These poles may be made from fiberglass, wood, or metal Plumb Bobs Made of brass and weighing 6 to 18 ounces, plumb bobs are frequently used in conjunction with a double pentagonal prism. The plumb bob is attached to the bottom of a string coming from the double prism, in order to mark exactly where a perpendicular is needed along a centerline. Gammon Reel Gammon reel is commonly used to place and adjust plumb bobs. It may also be used as a target when taping. In general, a gammon reel is little more than a strong reel of line that can be adjusted to account for various terrains when taking measurements using a plumb bob and double prism. Theodolites Theodolites are primarily used to measure horizontal and vertical angles though they can also be used to determine horizontal distances and elevations. Theodolites are primarily used by professional surveyors, though they are sometimes used in other disciplines like metrology and rocket launch technology. The theodolite features a movable telescope mounted between a horizontal and vertical axis. Theodolites that feature a telescope, which can be moved in a complete circle along a vertical plane are known as transit theodolites.

Theodolites that feature a telescope that can only rotate in a semi-circle are known as non-transit theodolites. Measuring Wheels Measuring wheels are designed to be pushed along by surveyors to measure specific distances. They feature a counter on bottom that determines the distances based on number of rotations. Though simple in form, when properly calibrated measuring wheels can provide highly accurate readings. Electronic Distance Measurer An electronic distance measuring device detects the distance from one point to another based on the amount of time it takes a laser to travel from the measuring device to a prism. These advanced, but common pieces of surveying equipment have largely replaced chains as the standard for measuring distance. Global Positioning System The Global Positioning System or GPS may is one example of an electronic distances measurer. However, GPS does not work well with every terrain, as it is difficult to pick up the necessary satellite signals in heavily wooded or mountainous areas. Total Station The device known as the total station is one of the most advanced forms or surveying equipment available. An all-in-one device, the total station is a form of electronic distance measurer that is used to automatically measure both horizontal and vertical distances, as well as the angle of various slopes.

Finding Surveying Equipment on eBay eBay sellers from around the world offer consumers a wide variety of surveying equipment to meet virtually all needs. To find a piece of surveying equipment on eBay, begin by inputting words related to what you need in the search engine atop any eBay page. For example, you might type " total station " or " measuring wheel ." After search results load, you can use various eBay refinement options to hone in on a precise item. Contacting the eBay Seller Once you have found the surveying equipment you desire, it may prove helpful to learn a little bit about the seller or ask questions about the product listed before making a commitment to buy. This can be easily accomplished through a visit to the eBay seller's profile page . From there, you can read feedback left from previous patrons, see what other items the seller has available, and send a message to the user regarding any questions that you may have. Conclusion Surveyors measure distances in order to build level, sound buildings or determine the boundaries of a piece of land. This profession, typically held by individuals with a degree in civil engineering, is a very important one that has existed for all of recorded human history.

Since distances can be distorted by hills and other factors, so the surveyor must use several unique tools to acquire precise measurements. The profession of surveying is commonly related to civil engineering, though surveying is an important part of many academic disciplines. The art of surveying requires a good working knowledge of math, physics, engineering, and even law. The professional surveyor will be highly trained in his or her field, capable of performing a multitude of measurements, using the various tools and equipment listed throughout this buying guide. Surveyors have, and likely always will be, an important part of developing infrastructure and maintaining a civilized society. Tags: How to Buy Surveying Equipment on eBay | eBay How to Buy Surveying Equipment on eBay Share 26 June 2013 If a person likes outdoor work and measuring, then surveying may be an appropriate career choice. The goal of surveying is to measure the distance, angles, and elevations of the earth. This information is often used to determine property lines and to build roads as well as for excavation sites for new buildings and other types of civil engineering projects. Surveyors are generally the first people on the scene of a new project to provide information on the land to be built upon.

While surveying dates back nearly 5000 years to ancient Egypt, recent advances in technology have dramatically changed the tools used in surveying. An overview of surveying equipment is provided, including the various types of tools that are available on eBay . Whether a person is an amateur surveyor or needs to buy his or her own equipment for a job, eBay has surveying equipment for every need. Prices on the site are also very competitive and new tools are constantly becoming available. A Brief History of Surveying Equipment The first recorded uses of surveying were from Ancient Egypt to form farm boundaries via a rope stretcher, which was the first type of surveyor. There is also evidence that surveyors were at the Great Pyramid of Giza as well as Stonehenge in England using rope geometry. In the Arab Empire during the rise of the Caliphate, surveyors used surveying equipment including a reed level, a rotating alhidade to provide accurate alignment, and a surveying astrolabe for measuring angles and triangulation. By the 18th century, surveyors in Europe used measuring tape, corner prisms, and red and white poles for surveying.

Land surveying was one of the first professions to have a license issued by the government. Types of Surveying Equipment Found on eBay There are many types of surveying equipment found on eBay. The following sections provide details of some of the major categories found on the site. The categories include total stations and accessories, levels and autolevels, transits and theodolites (which are essentially the same thing), tripods and grace rods, and others. Levels and Autolevels Levels used in surveying are not the type of tool used to measure the flatness of a surface (often used in contracting). This is one of the largest categories of surveying equipment found on eBay. These levels measure the elevation of a surface. A hand level is a common type of non-electronic tool. It has a metal sighting tube, which has a bubble tube on top. It uses a 45-degree mirror to reflect an image into the tool in order to see the landscape and the bubble. A level line of sight is found when the bubble is centered between the horizontal lines within the tube.

Abney Levels Like a hand level, an Abney level allows elevation measurements in addition to rudimentary vertical angle and slope measurements via the addition of a protractor on the bubble tube. When looking through the sighting tube, a split view is provided. Half of the view shows the bubble, while the other half shows the landscape and horizontal lines. Rotary Lasers A rotary laser is a type of laser level used in surveying or in home remodeling. A laser level is fixed in one place and provides a laser beam at a level point on horizontal and vertical areas. A rotary laser casts a laser beam in a 360-degree circle to show a laser chalk line on all areas. It is generally used indoors to hit walls, ceiling, and floor at the same time, but can be used in surveying applications. There are laser detectors that can be used when the laser light is not directly visible. Automatic Levels Automatic levels feature a self-leveling feature. The user provides a rough level using a three-screw leveling head, and then centers the bullseye bubble. After the bubble in manually centered, an automatic compensator levels the line of sight. The compensator also keeps the instrument level so that horizontal measurements can be made.

Torpedo Levels and Lasers Like a rotary laser, a torpedo level can also be used in carpentry and home remodeling as well as surveying. Torpedo is not a brand name, even though it sound like one, and torpedo levels can readily be found on eBay. The level is used to ensure that a surface or angle is level. The rectangular level has a vial in the middle that is filled with a liquid. Some torpedo levels have more than one vial to provide measurements for more than one angle simultaneously. Some torpedo levels are magnetized to provide better measurements for metal surfaces. Other torpedo levels include a laser to outline a straight line for some distance. Theodolites A theodolite (also known as a transit) was commonly used before the institution of total stations, but theodolites can still be found in abundance on eBay. It is an instruments used to measure angles of horizontal and vertical planes. Theodolites consist of a movable telescope mounted within two perpendicular axes: the horizontal (or trunnion) axis and the vertical axis. The theodolite uses triangulation to provide the angles. Some theodolites are also equipped with an infrared-based distance measuring device for measurement of three-dimensional vectors.

Total Stations Total stations are tools that have an electronic distance measuring device that can store readings and allow them to be downloaded to an external data collector, such as a handheld computer. The total station also has a microprocessor that allows for measurement of horizontal and vertical angles as well as slope distance. The processor also automatically calculates distances, elevations, and coordinates. Total stations on eBay come from manufacturers such as Leica, Geodimeter, Trimble, and Panasonic. Robotic and GPS-Incorporating Total Stations There are robotic total stations that allow for distance measurement by remote control to eliminate the need for more than one person to operate the total station. Some total stations can connect to GPS systems to provide quicker and more precise readings. GPS systems do not work well in areas with dense tree cover or in construction areas. The following table indicates how precise GPS readings are for total stations: Orientation Land Survey or Surveying Equipment: Used & New Construction GPS Surveying Instruments & Equipment Different Types of Surveying Equipment: Old and New written by: Raunekk • edited by: Lamar Stonecypher • updated: 1/31/2013 A surveyor depends on their equipment for acquiring accurate measurements quickly and easily.

The article describes the various types of surveying equipment, both ancient and modern, that are available in the market today. slide 1 of 4 Many kinds of surveying equipment have been used in the past and present to help a surveyor measure various parameters of a land area. Each of these parameters is measured by a specific type of measuring equipment. In this article we will learn about the importance of the main types of surveying equipments, both old and new. slide 2 of 4 Surveying Equipments - Old In ancient times surveying equipment included chains, compass, solar compass, transit, theodolite and more. Chains with equal size links were used to measure distance between two required points. A compass was used to measure the direction of a line that was being surveyed. A solar compass was used for measuring both the direction and latitude of a particular point with the help of sun and stars. A Solar Compass could also measure horizontal angles and the “true north" of a particular place. A metallic measuring tape was used to measure shorter distances. As technology gradually advanced with time, instruments used for surveying also improved. Horizontal and vertical angles were measured using a simple theodolite whereas different heights were measured by a basic level.

Measuring wheels were also initially used by surveyors to measure long distances in a short duration of time. Measuring wheels came in two types: mechanical and electrical, and both worked on the same principle of rolling the wheel from the start to the end point. In the early 1900s, surveyors started to use surveying equipment such as planimeters, theodolites, automatic levels and measuring wheels. A planimeter is the best known tool for measuring asymmetrical land areas as they eliminate the need for charts or manual calculations; whereas a theodolite allows measuring of horizontal and vertical angles. A theodolite consists of a movable telescope attached over perpendicular axis. It provides precise measurement of angles and is an integral part of every surveying tool kit. A transit is a type of theodolite but has less precision. An auto level or a dumpy level is also a type of surveying equipment used for measuring horizontal levels. It consists of a telescope like device fitted on a tripod stand. Auto level, tilting level, and self-leveling level are all types of leveling instruments, each providing different rotating capabilities. Most surveying instruments are fixed on a tripod, which acts as a support.

As the name suggests, tripods have three legs with length varying capability. Many of these equipments are still used by surveyors around the world. slide 3 of 4 Surveying Equipments - New Recent development in technology has provided some of the finest surveying equipments present today. Moreover, with the introduction of global positioning system, the methods of surveying have also totally changed. GPS has not only made surveying faster but has increased the accuracy to amazing heights. GPS works with the help of satellite systems which provide accurate data directly on the computer screen. Various types of GPS equipment is available, from basic to highly advanced. Some GPS equipment even have night vision which facilitates surveying during the night time. However, it is said that though GPS helps in acquiring the exact position of the land; it does not provide good results in dense forest areas or concrete constructions. For this reason, an instrument known as total station is used along with the GPS. Total station is a theodolite with an Electronic Distance Measurement Device. Total station has also been one of the reasons behind the drastic change of technology in the surveying field. EDMD shifted the surveying technology from optical mechanical devices to digital electronic devices.

In spite of just being distance measuring equipment, total station can also be used for leveling when adjusted in a horizontal plane. Most of the ultra-modern surveying devices are a combination of one or more of these devices. There is a long list of surveying equipment available in the market today. The selection of particular equipment depends on the type of application and accuracy required. Though all these equipment provide a wide range of options to surveyors, it is advisable to have a thorough knowledge of both, the equipment and the desired survey. This would not only help in bringing accuracy to the work but would also save considerable time and money. slide 4 of 4 NOAA 200th: Collections: Theodolites Collections Collections : Theodolites An Angular Point of View: A Photo Collection Illustrating the History of Theodolites at the National Geodetic Survey Used to measure horizontal and vertical angles, the theodolite remained the backbone of geodetic surveys from the 1800s until the early 1980s.

This collection of theodolites tells the story of the development and usage of the instrument, including some of the challenges faced by field parties, from the first fieldwork of Survey of the Coast Superintendent Ferdinand Hassler until today. Introduction Point A to Point B by way of angles and a measured distance. Distances measured for scale are referred to as base lines. Click image for larger view. Everyone has seen them - surveyors at a construction site or along a highway pointing what looks like a small telescope at a target. It is a small telescope, but they are not just looking at the scenery. Chances are, the surveyors are using a theodolite or transit to measure angles. By using the principles of trigonometry, the surveyors can use measured angles to figure out exactly where they are and where they (or the construction they are responsible for) are going. As its name indicates, triangulation is a type of surveying largely based on the measurement of angles and distances, which build a series of connected triangles from which the latitude and longitude (or plane coordinates) for points of the triangle are derived. Geodetic surveyors observe a star that has a known celestial position to determine a starting orientation.

Then, by carefully measuring a distance for scale, they can use the series of interconnected triangles to map and model the surface of the continent from coast to coast. This is exactly what the Survey of the Coast (and its descendants) has done…and then some! About this Collection This collection of eight images illustrates some of the history of the theodolite, an instrument that combines a fine-quality telescope with a finely subdivided circle that allows the reading of angle values as the telescope is turned. Used to observe both horizontal angles to build triangles and vertical angles to determine elevations, the theodolite remained the backbone of geodetic surveys from the first fieldwork of the Survey of the Coast in the 1800s until today's National Geodetic Survey (NGS) largely replaced triangulation and traverse work with global positioning system (GPS) surveys in the early 1980s. Theodolites are still an essential part of the "total" of the "total stations" used by crews of NGS's Aeronautical Survey Program and by many private surveyors.

The following collection of theodolites tells some of the story of the development and usage of the instrument, including some of the challenges faced by field parties, from the first fieldwork of Survey of the Coast Superintendent Ferdinand Hassler until today. You can browse through the instruments in the collection by clicking on the links to the right or click here to view the items in the Theodolites Collection . (top) Measuring Angles: Introduction Those who remember their high school geometry will find the core of geodetic surveying familiar: given a certain amount of information about the angles and lengths of the sides of a triangle, it is possible to calculate the remaining unknown lengths and angles of the triangle. Given this information and a beginning point whose coordinates are already known (X, Y in plane coordinates and on the high school pop quiz; latitude and longitude at NGS), it is possible to build a framework that allows the calculation of new points by the measurement of new angles and distances. Classical, non-GPS geodetic surveyors measured those angles and distances with highly accurate equipment and techniques and performed calculations based on the reality that the measurements were performed on the curved surface of the Earth.

Before the advent of electronic distance measuring instruments, surveyors used tapes made of an alloy called "invar," to measure base lines. Click image for larger view. In classical surveying, a line-of-sight is necessary between stations, since it is necessary to carefully sight on or align with a target during measurements. Until the 1950s, when electronic distance measurement was adopted, it was also necessary to measure the distances on a line, called a base line, which had been carefully cleared, graded, and leveled. The distances were then measured by carefully moving metal bars or tapes, usually 5 to 50 meters in length, end-to-end along the complete distance of the base line. Precise measurements of base lines that were typically 6 to 12 miles in length would often take several weeks to complete. Using a Theodolite Basic use of a theodolite required that the instrument be mounted on a stable tripod or stand and be carefully plumbed over the survey station that was to be occupied and observed from. The theodolite was then leveled. In this photo from 1915, one surveyor looks through the telescope of a theodolite while his partner records angle measurements.

Click image for larger view. The observer looked through the telescope and carefully aligned the vertical cross-hair with the left-most survey target. The horizontal circle was rotated so that it read just above zero when the cross-hairs were on this target. The circle was then locked in place and the direction indicated on the circle was read and recorded. After this reading was taken, the telescope was rotated clockwise until the cross-hair was aligned with a second target. This second direction was read from the circle and recorded. This procedure was repeated until all targets were observed and recorded. Then, the telescope was rotated 180 degrees around both axes. The same stations were observed again and the angle values recorded. This entire procedure was one set of angles. The two readings for each target were averaged to help eliminate systematic errors. The number of sets of angles observed depended on the precision of the survey work being performed. For first-order survey work, 16 sets were observed and averaged to determine the final angles. Directions exceeding a specified value from the mean were rejected and repeated. (top) Background: A Brief History of "Turning Angles" We have been measuring angles for surveying and construction for centuries.

In building the great pyramids, Egyptians used an instrument called a "groma" to measure angles. Records indicate that the Romans used these tools as well. Roman surveyors also used a device called a "dioptra," which was an instrument that had a circular plate marked in angles. The instruments used for the measurement of angles have evolved considerably from the groma and dioptra, with the developmental emphasis on marking and reading the subdivisions used to determine angles. In 1571, Leonard Digges described a "theodolitus," which was not quite what we now understand as a theodolite: a divided circle and square having a compass in the center, it lacked the familiar telescope of today. By the mid-1700s, the more familiar telescope mounted with a horizontal circle and vertical semi-circle was being produced. Hand crafted of brass, with the angles also scribed by hand, theodolites of the era are virtually works of art. However, because the angles were scribed by hand, they were only as accurate as the capabilities of the person who made them. This was critical: an error of one second in a triangle translates into one foot at a distance of 40 miles.

Early theodolites had expected errors of several minutes. Englishman Jesse Ramsden's mechanical dividing engine was an enormous leap forward when invented in 1773. With its higher production and accuracy, the dividing engine replaced the slowness and possibility of human error associated with hand scribing. The dividing engine dramatically increased the availability of precision surveying and navigation instruments and placed England in the forefront of the production of such instruments. Hassler's first series of triangles. Note the extent of New York City in 1817. Secondary triangles were observed to fill in the map. Click image for larger view. When Ferdinand Hassler was appointed Superintendent of the Survey of the Coast by Thomas Jefferson in 1807, he was already known for triangulation in his native Switzerland. When asked by Congress if another (cheaper) method than triangulation could be used to map the United States, Hassler replied with a thoroughly explained "No." He noted that many countries of Europe had already been mapped by triangulation, many before 1800.

It was to England that Hassler sailed with the blessings of Congress in August of 1811, seeking the best surveying equipment possible for the fledgling Survey of the Coast. He returned to the United States in October of 1815, having been stranded as an enemy alien during the War of 1812. He did, however, manage to obtain the high-quality instruments, many of his own design, he had sought. Hassler's demand for the proper equipment to do the best job possible never faltered. His legacy, and the inventiveness and skill to design and build what could not be bought, was passed to the Coast and Geodetic Survey and still lives on today in its "descendent," the National Geodetic Survey. Contributed by Cindy Craig, NOAA's National Ocean Service Theodolite vs. the Total Station: Southern Photo Presents a Brief History of Surveying Equipment Theodolite vs. the Total Station: Southern Photo Presents a Brief History of Surveying Equipment Share Article Before the advent of the electric total station, surveyors used an instrument known as a theodolite to measure angles and calculate distance.

How does this purely mechanical piece of surveying equipment work and how does it compare the the electronic, computer driven total station that replaced it? Southern photo has gathered the following brief history of surveying equipment to shed some light on the differences between these two tools. Greensboro, NC (PRWEB) April 30, 2007 Before the advent of the electric total station, surveyors used an instrument known as a theodolite to measure angles and calculate distance. How does this purely mechanical piece of surveying equipment work and how does it compare the the electronic, computer driven total station that replaced it? Southern photo has gathered the following brief history of surveying equipment to shed some light on the differences between these two tools. Mark Cheves, editor of The American Surveyor magazine, says that there are really only two situations in which to use a theodolite today. In the third world, where access to electricity is spotty or nonexistent, theodolites are a natural alternative to the electric-powered total station. It can do this because intead of using computer driven measurements and calculations, the theodolite employs two discs, one on the vertical and one on the horizontal plane, that are manually rotated to set an angle.

The surveyor then reads the angle using a tiny microscope attached to the side of the instrument. Also, in the construction industry, if a contractor needs to square off a building or create a simple diagonal line, a theodolite can measure a 45- or 90-degree angle fairly easily, without the added complication of using a total station with a prism and a computer. Cheves also said there are some surveyors who like the traditional feel of a theodolite, and use it because of some closely held beliefs. In the early 1900s, before electric total stations and GPS technologies were available, surveyors had to use either a theodolite or even a compass and chain to measure angles, distances and borders. Since this was the only technology available, and state governments had to create official land boundaries for businesses and citizens, measurements taken by surveyors using these instruments were made official in governmental logs. Some highly traditional thinkers in the surveying industry, Cheves said, believe that in order to arrive at these early official borders, one must use the same instruments they had available back then. Total station technology has assisted surveyors in several ways. One, it has eliminated human error to a large extent.

With a theodolite, the surveyor must peer through a tiny microscope to see the angle, and then write it down correctly in his log book. The total station records this data, which the surveyor simply downloads onto his computer when he returns to his office. Second, the total station has completely eliminated the need to measure lines by hand. In the past, surveyors had to use chain to mark off lines, and then count the links to measure the distance with the most accuracy. Chains are unreliable because they can lose links in transit and they change shape in very hot or cold weather, and a surveyor's goal is to get a measurement down to within a few centimeters. Third, the total station can be set up on a tripod, allowing for a one-man surveying crew. Surveyors are difficult to come by these days. Cheves said surveying used to be a learned trade. He's been surveying since 1963 and he does not have a college degree. Now, 23 states require a four-year degree and surveyors must sit for both a national and state examination before they can work in the field. Since this is the case, many states are losing surveyors as they retire.

If a company only has six people on staff, now it can send out a one-man operation. Theodolites still have a place in the surveying industry, where electricity is sparse or when one only needs to measure a simple angle, but since the 1970s they have been almost completely replaced by the electronic total station. Old-school surveyors still keep them around, but the elimination of so much error and additional work makes the total station and GPS technology extremely attractive to surveyors today. You can find a wide variety of total stations and other surveyors' equipment at . About SouthernPhoto.com: Southern Photo Inc. is a supplier of surveying equipment. We also offer repair and maintenance at our full service repair shop specializing in Topcon service and repair. In addition to surveying equipment and supplies, SouthernPhoto.com also offers drafting supplies and furniture and art supplies. For more information, visit .

# # # 5.5 Land Surveying and Conventional Techniques for Measuring Positions on the Earth’s Surface | GEOG 260: Mapping our Changing World 5.5 Land Surveying and Conventional Techniques for Measuring Positions on the Earth’s Surface Print Ease, accuracy, and worldwide availability have made ‘GPS’ a household term. Yet, none of the power or capabilities of GPS would have been possible without traditional surveyors paving the way. The techniques and tools of conventional surveying are still in use and, as you will see, are based on the very same concepts that underpin even the most advanced satellite-based positioning. Geographic positions are specified relative to a fixed reference. Positions on the globe, for instance, may be specified in terms of angles relative to the center of the Earth, the equator, and the prime meridian. Land surveyors measure horizontal positions in geographic or plane coordinate systems relative to previously surveyed positions called control points, most of which are indicated physically in the world with a metal “benchmark” that fixes the location and, as shown here, may also indicate elevation about mean sea level (Figure 5.10).

In 1988 NGS established four orders of control point accuracy, ranging in maximum base error from 3mm to 5cm. In the U.S., the National Geodetic Survey (NGS) maintains a National Spatial Reference System (NSRS) that consists of approximately 300,000 horizontal and 600,000 vertical control stations (Doyle,1994). Doyle (1994) points out that horizontal and vertical reference systems coincide by less than ten percent. This is because: ....horizontal stations were often located on high mountains or hilltops to decrease the need to construct observation towers usually required to provide line-of-sight for triangulation, traverse and trilateration measurements. Vertical control points however, were established by the technique of spirit leveling which is more suited to being conducted along gradual slopes such as roads and railways that seldom scale mountain tops. (Doyle, 2002, p. 1) You might wonder how a control network gets started. If positions are measured relative to other positions, what is the first position measured relative to? The answer is: the stars.

Before reliable timepieces were available, astronomers were able to determine longitude only by careful observation of recurring celestial events, such as eclipses of the moons of Jupiter. Nowadays, geodesists produce extremely precise positional data by analyzing radio waves emitted by distant stars. Once a control network is established, however, surveyors produce positions using instruments that measure angles and distances between locations on the Earth's surface. Figure 5.10: Benchmark used to mark a vertical control point. Credit: Thompson, 1988. 5.5.1 Measuring Angles and Distances You probably have seen surveyors working outside, e.g., when highways are being realigned or new housing developments are being constructed. Often one surveyor operates equipment on a tripod while another holds up a rod some distance away. What the surveyors and their equipment are doing is carefully measuring angles and distances, from which positions and elevation can be calculated. We will briefly discuss this equipment and their methodology. Let us first take a look at angles and how they apply to surveying.

Although a standard compass can give you a rough estimate of angles, the Earth’s magnetic field is not constant and the magnetic poles, which slowly move over time, do not perfectly align with the planet’s axis of rotation; as a result of the latter, true (geographic) north and magnetic north are different. Moreover, some rocks can become magnetized and introduce subtle local anomalies when using compass. For these reasons, land surveyors rely on transits (or their more modern equivalents, called theodolites) to measure angles. A transit (Figure 5.11) consists of a telescope for sighting distant target objects, two measurement wheels that work like protractors for reading horizontal and vertical angles, and bubble levels to ensure that the angles are true. A theodolite is essentially the same instrument, except that it is somewhat more complex and capable of higher precision. In modern theodolites, some mechanical parts are replaced with electronics. Figure 5.11: A traditional transit once used by surveyors. Credit: Raisz, 1948, Used by permission. When surveyors measure angles, the resultant calculations are typically reported as either azimuths or bearings, as seen in Figure 5.12.

A bearing is an angle less than 90° within a quadrant defined by the cardinal directions. An azimuth is an angle between 0° and 360° measured clockwise from North. "South 45° East" and "135°" are the same direction expressed as a bearing and as an azimuth. Figure 5.12: Azimuths and Bearings. Note that an azimuth of 360° is the same as 0°. Credit: Department of Geography, The Pennsylvania State University. 5.5.2 Measuring Distances To measure distances, land surveyors once used 100-foot long metal tapes that are graduated in hundredths of a foot. An example of this technique is shown in Figure 5.13. Distances along slopes were measured in short horizontal segments. Skilled surveyors could achieve accuracies of up to one part in 10,000 (1 centimeter error for every 100 meters distance). Sources of error included flaws in the tape itself, such as kinks; variations in tape length due to extremes in temperature; and human errors such as inconsistent pull, allowing the tape to stray from the horizontal plane, and incorrect readings.

Figure 5.13: Surveying team measuring a baseline distance with a metal (Invar) tape. Credit: Hodgson, 1916. Since the 1980s, electronic distance measurement(EDM) devices have allowed surveyors to measure distances more accurately and more efficiently than they can with tapes. To measure the horizontal distance between two points, one surveyor uses an EDM instrument to shoot an energy wave toward a reflector held by the second surveyor. The EDM records the elapsed time between the wave's emission and its return from the reflector. It then calculates distance as a function of the elapsed time (not unlike what we’ve learned about GPS!). Typical short-range EDMs can be used to measure distances as great as 5 kilometers at accuracies up to one part in 20,000, twice as accurate as taping. Instruments called total stations (Figure 5.14) combine electronic distance measurement and the angle measuring capabilities of theodolites in one unit. Next we consider how these instruments are used to measure horizontal positions in relation to established control networks. Figure 5.14: A modern total station. Credit: Łukasz Fus.

5.5.3 Combining Angles and Distances to Determine Positions Surveyors have developed distinct methods, based on separate control networks, for measuring horizontal and vertical positions. In this context, a horizontal position is the location of a point relative to two axes: the equator and the prime meridian on the globe, or to the x and y axes in a plane coordinate system. We will now introduce two techniques that surveyors use to create and extend control networks (triangulation and trilateration) and two other techniques used to measure positions relative to control points (open and closed traverses). Surveyors typically measure positions in series. Starting at control points, they measure angles and distances to new locations, and use trigonometry to calculate positions in a plane coordinate system. Measuring a series of positions in this way is known as "running a traverse." A traverse that begins and ends at different locations, in which at least one end point is initially unknown, is called an open traverse. A traverse that begins and ends at the same point, or at two different but known points, is called a closed traverse.

"Closed" here does not mean geometrically closed (as in a polygon) but mathematically closed (defined as: of or relating to an interval containing both its endpoints). By "closing" a route between one known location and another known location, the surveyor can determine errors in the traverse. Measurement errors in a closed traverse that connects at the point where it started can be quantified by summing the interior angles of the polygon formed by the traverse. The accuracy of a single angle measurement cannot be known, but since the sum of the interior angles of a polygon is always (n-2) × 180, it's possible to evaluate the traverse as a whole, and to distribute the accumulated errors among all the interior angles. Errors produced in an open traverse, one that does not end where it started, cannot be assessed or corrected. The only way to assess the accuracy of an open traverse is to measure distances and angles repeatedly, forward and backward, and to average the results of calculations. Because repeated measurements are costly, other surveying techniques that enable surveyors to calculate and account for measurement error are preferred over open traverses for most applications.

5.5.4 Triangulation Closed traverses yield adequate accuracy for property boundary surveys, provided that an established control point is nearby. Surveyors conduct control surveys to extend and add point density to horizontal control networks. Before survey-grade satellite positioning was available, the most common technique for conducting control surveys was triangulation (Figure 5.16). Figure 5.15: Establishing new control points by triangulation from an existing control point (A). Credit: Department of Geography, The Pennsylvania State University. Adapted from DiBiase's original text (1997). Using a total station equipped with an electronic distance measurement device, the control survey team commences by measuring the azimuth alpha, and the baseline distance AB. These two measurements enable the survey team to calculate position B as in an open traverse. The surveyors next measure the interior angles CAB, ABC, and BCA at point A, B, and C. Knowing the interior angles and the baseline length, the trigonometric "law of sines" can then be used to calculate the lengths of any other side. Knowing these dimensions, surveyors can fix the position of point C.

Having measured three interior angles and the length of one side of triangle ABC, the control survey team can calculate the length of side BC. This calculated length then serves as a baseline for triangle BDC. Triangulation is thus used to extend control networks, point by point and triangle by triangle. 5.5.5 Trilateration An alternative to triangulation is trilateration, which uses distances alone to determine positions. By eschewing angle measurements, trilateration is easier to perform, requires fewer tools, and is therefore less expensive. Having read this chapter so far, you have already been introduced to a practical application of trilateration, since it is the technique behind satellite ranging used in GPS. You have seen an example of trilateration in Figure 5.8 in the form of 3-dimensional spheres extending from orbiting satellites. Demo 1 below steps through this process in two dimensions. Try This: Step through the process of 2-dimensional trilateration. Demo 1: Trilateration in two dimensions. This demonstration requires the Adobe Flash plugin. If you do not have this plugin, it can be downloaded from Adobe for free at: . Credit: Joshua Stevens, Department of Geography, The Pennsylvania State University.

Once a distance from a control point is established, a person can calculate a distance by open traverse, or rely on a known distance if one exists. A single control point and known distance confines the possible locations of an unknown point to the edge of the circle surrounding the control point at that distance; there are infinitively many possibilities along this circle for the unknown location. The addition of a second control point introduces another circle with a radius equal to its distance from the unknown point. With two control points and distance circles, the number of possible points for the unknown location is reduced to exactly two. A third and final control point can be used to identify which of the remaining possibilities is the true location. Trilateration is noticeably simpler than triangulation and is a very valuable skill to possess. Even with very rough estimates, one can determine a general location with reasonable success. Practice Quiz Registered Penn State students should return now to the Chapter 5 folder in Canvas to take a self-assessment quiz Land Surveying. You may take practice quizzes as many times as you wish. They are not scored and do not affect your grade in any way.

Question: Formerly used in navigation, and now a tool used in surveying, a theodolite is used to measure what?
Answer: Angles